Here's a simple example. The new keys are "id", "response", and "response_only" (their descriptions are in the attribute reference):

[dialog]
topic=New quest
response=quest_accept
response=quest_refuse
him=Do you accept?

[dialog]
id=quest_accept
topic=Yes
response_only=true
you=I accept.

[dialog]
id=quest_refuse
topic=No
response_only=true
you=I refuse.